In the past, there have been various network systems (e.g., home appliance managing systems). The home appliance managing system includes central managing devices and a center server. The central managing device is configured to monitor and control one or more home appliances (e.g., control panels, lighting equipment, air conditioning equipment, and various security devices) installed in a residence. The center server is connected to the central managing devices via the Internet. The center server is configured to store various data. The central managing device obtains data from the center sever in response to a request from the home appliance, and sends the obtained data to the home appliance. The home appliance provides a predetermined service (monitoring the status of the home appliance, controlling turning on and off the lighting equipment, controlling turning on and off the air conditioning equipment, and locking and unlocking an electrical lock) to a user on the basis of the data obtained from the center server via the central managing device.
However, when the home appliance provides a service (e.g., a display control user interface) to a user with high speed response, the home appliance needs to access the center server via the central managing device for obtaining the data each time the user requests, and therefore requires much time for completion of the service and suffers from lowered response.
In view of the above, there has been provided a technique to provide a cache memory to a device (e.g., central managing devices) on the network (JP 11-112541 A). The cache memory is configured to store (cache) once obtained data, as cache data. In this arrangement, when the home appliance requests the same data, the central managing device can send the cache data to the home appliance without accessing the center server.
However, the central managing device cannot obtain the cache data unless the home appliance requests the data once at least. Therefore, with regard to the data which the home appliance has not requested, the central managing device needs to access the center server. Consequently, it is difficult to exhibit the sufficient response speed.